Remove unneeded bootimage properties

These were added as part of http://r.android.com/731514, but
most of these properties make no sense for the bootimage. Revert
to only defining date, date.utc and fingerprint.

Bug: 131066061
Test: inspect vendor/build.prop
Test: boot, no SELinux warnings for removed props
Change-Id: Ibbeff9870a5b71e83c2cceeb1327b12600077b23
Merged-In: Ibbeff9870a5b71e83c2cceeb1327b12600077b23